In situ observation of optically and thermally induced charge depletion in chromophore-doped cyclic olefin copolymers

For a number of years, cyclic olefin copolymers (COC) have been known for their good charge-storing properties. Due to their high optical transparency, they are ideally suited to study the interaction of trapped space charges with light. Films of different COC grades were doped with various chromophores and studied using thermally stimulated discharge (TSD) and photostimulated discharge (PSD). The space charge profiles were determined in real time using the thermal pulse (TP) technique, where the low-transparency top electrode is heated with a short laser pulse. UV irradiation near 300 nm leads to an accelerated decay of the near-surface charge density, which can be explained if at least part of the space charges are released from traps with a depth of approx. 4 eV. In addition, the thermal diffusivity was determined from laser-induced temperature phase shifts.